The separation of solids from liquids creates many problems in obtaining both adequate separation of the solids and the liquids and at the same time an adequately long service life of the equipment without an unnecessarily high consumption of power during operation. One known centrifugal separator for this purpose, which is adapted for separating, for example, water from a slurry of solid particles in water, comprises a rotatable imperforate hollow centrifuge drum at least a part of which is tapered and the axis of which coincides with the axis of rotation of the drum, a conveyor coaxially located within the centrifuge drum and itself rotatable in the same direction as the centrifuge drum at a speed above or below that of the centrifuge drum such that the differential speed of the two is small in relation to the absolute speed of rotation thereof whereby to convey material in the space between the drum and the conveyor axially thereof as a result of the differential speed of rotation towards the narrow end of the tapered part of the drum, and means for introducing a solids-liquids mixture to be separated into the said space.
In such known equipment the conveyor may comprise a scroll (by which term is meant a continuous helical screw conveyor) or a plurality of individual blades and, in this latter case, each individual blade acts in the same way as an elementary portion of the scroll to displace the solids fraction axially: as will be appreciated, under the centrifugal action of the rotating drum the denser solids particles in the solids-liquids mixture to be separated migrate radially outwardly towards the surface of the drum and the liquid forms a pool at the wider end of the drum which, conventionally, incorporates a right-circular cylindrical portion maintained by a radially inwardly directed lip forming a weir over which the liquid flows for collection in a launder.
One of the problems encountered in operating known such centrifugal separating apparatus lies in the fact that, due to the difficulty of obtaining sufficiently precise manufacturing tolerances, the scraper blades are usually a clearance fit within the drum so that there is a narrow space between the active edge of the blade and the surface of the drum in which a thin film of solid particles can collect. This layer of particles, termed the "heel" is effectively pinned to the surface of the drum by the centrifugal action thereof and is not subjected to the axial displacement of the blades which pass over it. The surface roughness of this layer of material is, however, very high and, furthermore, new solids particles which are continually being introduced to the drum during use build up onto this layer so that the blades have to exert a shearing action separating freshly-settled particles of the solids layer from the "heel" and this causes very heavy wear on the blades themselves so that they have an extremely short service life even if made from a highly wear-resistant material such as silicon carbide.